I've killed them with #4 buckshot (Hevi shot's "Heavy Duty" load) and they have most all been DRT. I did have to shoot one a second time, but my first shot was at about 45 yards and that is pushing the limits of that load in my gun.

The most lethal I have used was a 1 oz slug as I was setting up for a 3 gun competition. The slug was all that I had nearby and it was an opportunistic kill.